Element mounting substrate and semiconductor module

ABSTRACT

Conventional printed circuit boards had a problem of being inferior in heat-radiation characteristic, and metal-core printed circuit boards adopted to improve the heat-radiation characteristic had problems in having low rigidity and a tendency to bend. The ductility of the metal can be obstructed, and the metal protected; by covering substantially the whole area of the front and back sides of the metal core, consisting of metal as the main material, with a first ceramic film and a second ceramic film that obstruct the ductility of the aforementioned metal-core; and covering each of the ceramic films with insulated resin films, to cover the fragility of these ceramics.

FIELD OF THE INVENTION

The present invention relates to an element mounting substrate and a semiconductor module in which a semiconductor element is mounted on an element mounting substrate.

DESCRIPTION OF THE RELATED ART

Recently, a cell-phone, a small computer, and so on are required to be further miniaturized, accordingly a semiconductor device and a semiconductor module are reduced in weight, thickness, length, and size. In a set incorporating the semiconductor device and the semiconductor module, many ICs are incorporated into a limited small volume, and therefore, a heat dissipation problem occurs. Further, since the semiconductor device and the semiconductor module aim more functions and a higher current in the small volume, the heat dissipation problem occurs.

Hereinafter, the conventional structure will be described with reference to FIG. 7.

FIG. 7 illustrates a semiconductor device 100 employing an element mounting substrate comprising a metal core. FIG. 7A is a plan view of the semiconductor device. FIG. 7B is a cross-sectional view along A-A′ line of the semiconductor device. The element mounting substrate employs a metal core 101 at the center as the core, and the front surface side is coated with an insulating resin 102A, and the rear surface side is coated with an insulating resin 102B. In the element mounting substrate, conductive patterns 103A and 103B are provided respectively on the insulating resins 102A and 102B. In this case, there is provided a double-layered structure in which the insulating resin layers 102A and 102B and the conductive patterns 103A and 103B are formed on the front and rear sides; however, the conductive patterns may be further stacked to provide a four-layered structure, a six-layered structure, or more.

A semiconductor element 104 such as an LSI is secured to the element mounting substrate through a solder ball 106 formed corresponding to the conductive pattern 103A, and an insulating resin film 105 seals to cover the semiconductor element 104 while remaining a periphery of the element mounting substrate, whereby the semiconductor device 100 is formed. The semiconductor device 100 employing the element mounting substrate comprising the metal core thus has the effect of diffusing heat generated from the semiconductor element 104 through the metal core 101 and thereby reducing the temperature of the semiconductor element 104.

In FIG. 7, in order to reduce the thickness of the entire semiconductor device 100 as much as possible, the semiconductor element 104 is made face-down to be mounted. In this case, the heat emitted from the semiconductor element 104 is emitted to the metal core 101 through the solder ball 106 and the conductive pattern 103A, so that the temperature of the semiconductor element 104 is less likely to be reduced. Namely, since the flow of heat from the semiconductor element 104 is regulated by the solder ball 106 which is a neck portion, the temperature of the semiconductor element 104 is less likely to be reduced.

FIG. 8 shows a semiconductor device (semiconductor module) mounted with the semiconductor element.

FIG. 8A shows a structure of a semiconductor module 100A mounted with the face-up semiconductor element 104. Because of the face-up mounting, the thickness of the semiconductor module 100A itself is increased by the height of a thin metallic wire 107. However, in comparison with the case where the rear surface of the semiconductor element 104 is connected to the element mounting substrate by the solder ball, the semiconductor element 104 is secured in a larger area, and therefore, the temperature of the semiconductor element 104 is significantly reduced in comparison with the case of mounting the semiconductor element in FIG. 7.

FIG. 8B shows a semiconductor module 100B that is not coated with the insulating resin film 105, and passive elements such as a semiconductor element and a chip capacitor are mounted on the element mounting substrate. In the present view, although the semiconductor element 104 is secured using the thin metallic wire, the semiconductor element 104 maybe secured through a bump as shown in FIG. 7.

PRIOR ART DOCUMENTS Patent Documents

WO 2008/069260

Japanese Patent Application Laid-Open No. 2004-31732

Japanese Patent Application Laid-Open No. 63-72180

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

As described above, when a heat radiation property is required in a slimline package and a module employing a substrate, a metal core substrate is preferably employed. However, as the metal core, Cu is mainly employed, and the thickness is approximately 250 μm to 500 μm. Accordingly, in a double-layered conductive pattern and a four-layered conductive pattern, the thickness is approximately 1 mm, and therefore, the metal core is easily plastically deformed. Once a metal is plastically deformed, the metal cannot be returned to the original shape unless it is deformed again in the opposite direction, and therefore, this leads to reduction in yield in a manufacturing process. In finished products, the reliability may be reduced. Further, a difference of a thermal expansion coefficient α between an insulating resin and Cu causes warpage. The warpage is generated in a direction shown by the curved arrow in FIG. 8. In addition, each thermal expansion coefficient is different depending on materials. For example, the thermal expansion coefficient of the insulating resin film is 10 to 15 ppm, the thermal expansion coefficient of the substrate is 13 to 15 ppm in the X and Y directions and 23 to 33 ppm in the Z direction, and the thermal expansion coefficient of Si is 2.5 ppm. Thus, the reliability of the semiconductor element itself is reduced. Accordingly, a substrate that can maintain the flatness as much as possible is preferably used.

Means for Solving the Problems

In view of the above problems, the present invention provides an element mounting substrate comprising a metal core mainly composed of metal, a first ceramic film formed on one main surface of the metal core, a second ceramic film formed on the other main surface of the metal core, a first insulating resin film formed on a surface of the first ceramic film, a second insulating resin film formed on a surface of the second ceramic film, a first conductive pattern provided on a surface of the first insulating resin, and a second conductive pattern provided on a surface of the second insulating resin film. The element mounting substrate is characterized in that the first ceramic film and the second ceramic film have a smaller thermal expansion coefficient than the metal core and at the same time have a higher rigidity than the metal core.

Effect of the Invention

As described above, by virtue of the provision of the first ceramic film and the second ceramic film formed on the substantially entire area of the front and rear sides of the metal core mainly composed of metal, ductility of a metal core substrate is prevented. Further, by virtue of the provision of the first insulating resin film and the second insulating resin film coated on the substantially entire area on the front side of the first ceramic film and the rear side of the second ceramic film, brittleness of the ceramic film can be protected.

Since the ceramics and the insulating film are substantially symmetrically formed on the front and rear sides of the metal core as the center, warpage of the element mounting substrate can be suppressed.

Accordingly, in the semiconductor module and the semiconductor device mounted on the element mounting substrate, the flatness is improved, and, at the same time, the heat radiation property can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view of an element mounting substrate according to a first embodiment of the present invention;

FIG. 2 is a view of an element mounting substrate according to a second embodiment of the present invention;

FIG. 3 is a view of an element mounting substrate and a semiconductor module according to one embodiment of the present invention;

FIG. 4 is a view of an element mounting substrate and a semiconductor module according to one embodiment of the present invention; FIG. 5 is a view of an element mounting substrate and a semiconductor module according to one embodiment of the present invention;

FIG. 6 is a view of an element mounting substrate and a semiconductor module according to one embodiment of the present invention;

FIG. 7 is a view of a conventional semiconductor device;

FIG. 8 is a view of a conventional semiconductor device;

FIG. 9 is a view for explaining a manufacturing method of the present invention;

FIG. 10 is a view for explaining the manufacturing method of the present invention;

FIG. 11 is a view for explaining the manufacturing method of the present invention;

FIG. 12 is a view for explaining the manufacturing method of the present invention;

FIG. 13 is a view of an element mounting substrate according to one embodiment of the present invention;

FIG. 14 is a perspective view for explaining a method of observing a surface of an alumina film; and

FIG. 15 is a SEM photograph in which the surface of the alumina film is observed.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described. First, a summary of the present application will be described.

An element mounting substrate 1 has a metal core 2 and a metal core substrate M constituted of a ceramic film CEa formed on a front surface of the metal core 2 and a ceramic film CEb formed on a rear surface of the metal core 2. The ceramic films CE may be formed by applying a ceramic material to the metal core 2 or may be formed by applying chemical treatment to the metal core 2. An insulating resin film 4A is formed on a surface of the ceramic film CEa, and an insulating resin film 4B is formed on a surface of the ceramic film CEb. Further, a conductive pattern 5A is formed on a surface of the insulating resin film 4A, and a conductive pattern 5B is formed on a surface of the insulating resin film 4B.

Although the element mounting substrate shown here has a structure of double-layered conductive patterns including the front and rear sides, the element mounting substrate may be a multilayer substrate with four layers, six layers, or more provided by repeatedly stacking the insulating resin film and the conductive pattern.

Metal has the property of not returning to the original shape after being plastically deformed. Thus, in order to improve the flatness of the metal core employing metal, the ceramic films CE are arranged on the both sides of the metal core in the present invention. Since the ceramic film CE has a high rigidity and thus is less likely to be deformed, the warpage due to the plastic deformation of the metal core can be prevented. Meanwhile, brittleness peculiar to ceramic is solved by arranging the insulating resin films on the front and rear sides.

As viewed from the cross section of the element mounting substrate, in the element mounting substrate, the ceramic film and the insulating resin layer with the same material and thickness are symmetrically arranged on the front and rear sides of the metal core as the center. Thus, the extending ways on the front side and the rear side are the same, and in view of this, the warpage can be prevented.

The metal used as a core material includes metal mainly composed of Cu or Al, for example. Since the metal mainly composed of Cu has a high level of heat radiation property, the metal is suitably used in a power system module handling a high current. Meanwhile, although the metal mainly composed of Al is inferior to Cu, the metal has a high level of heat radiation property. Particularly in the case of Al, the weight is smaller than Cu, and, in addition, a film formed by self-oxidation and self-generation (aluminum oxide, alumina film) has a high level of resistance and rigidity; therefore, the metal mainly composed of Al is suitably used when flatness and heat radiation property are required at the same time.

As the ceramic film, an alumina film is suitably used. When a metal material mainly composed of Al is used, the alumina film can be formed in a self-generating manner by an anodic oxidation method, for example. In the alumina film formed by the anodic oxidation method, γ alumina is an amorphous film in general. As the alumina film, α alumina is suitably used. α alumina has a high level of chemical stability and mechanical strength because of the crystal structure, and the electrical insulation resistance is large. As one method of forming alumina, there is a submerged plasma process. Since the alumina film formed by the submerged plasma process has a microcrystalline structure, the brittleness is low. Further, since such a porous layer that is formed in the alumina film when the alumina film is formed by the anodic oxidation method, for example, is not generated, fine alumina pieces are less likely to be generated at the time of cutting. Thus, as the ceramic film formed on a surface of the metal material, alumina with no porous layer is used, whereby scattering of ceramic pieces can be suppressed when a through-hole is formed or a substrate is diced into individual pieces, and fabrication yield can be improved.

It is preferable that the thickness of the ceramic film is larger than the film thickness of the metal material used as the core material. The thickness of the ceramic film is increased, whereby a good high-frequency property as a feature of a ceramic substrate can be enjoyed, and, in addition, a metal material thinner than the ceramic film is provided between the ceramic films, whereby a substrate having a high level of impact resistance can be provided. It is preferable that the thickness of an internal metal material is not less than 50 μm. If the thickness is smaller than this value, the impact resistance cannot be obtained. Further, it is preferable that the thickness of the internal metal material is not more than 500 μm. If the thickness is larger than this value, the entire thickness of the element mounting substrate is increased, and therefore, it is undesirable.

The element mounting substrate 1 has through-holes 3. When the ceramic film CE is formed in a self-generating manner as described above, the ceramic film CE can be easily formed on a side wall of the through-hole 3.

A specific structure will be described using FIG. 1.

FIG. 1A shows a first embodiment of an element mounting substrate of the present invention and is an exploded cross-sectional view for explaining a constitution of the element mounting substrate as viewed from the cross section along A-A line of FIG. 1B. FIG. 1B is a perspective views of the element mounting substrate of the present invention as viewed in a planar manner. FIG. 2 shows a second embodiment of the element mounting substrate of the present invention. FIG. 2A is an exploded cross-sectional view for explaining a constitution of the element mounting substrate as viewed from the cross section along A-A line of FIG. 2B. FIG. 2B is a perspective view of the element mounting substrate of the present invention as viewed in a planar manner.

A difference between the first embodiment shown in FIG. 1 and the second embodiment shown in FIG. 2 will be described. In the first embodiment shown in FIG. 1, a single metal core substrate M is provided on the entire area of the element mounting substrate 1 or the substantially entire area except for some amount of margin MG. As upper and lower contacts, the through-holes 3 are provided in a portion of the single metal core substrate M, and the upper and lower portions are in contact with each other through the through-holes 3. The detail will be described later with reference to FIG. 3.

Meanwhile, in the second embodiment shown in FIG. 2, the metal core substrate M is provided on the entire area or the area except for the margin MG, and the metal core substrate M is not the single metal core substrate shown in FIG. 1, but the metal core substrate M is constituted of metal core substrates MA, MB, and the following metal core substrates as a plurality of pieces. The metal core substrates are separated in the form of an island and arranged on substantially the same plane. Extracted portions of electrodes on the front and rear sides of the element mounting substrate are connected through the through-hole 3 between the two metal cores MA and MB. The detail will be described later with reference to FIG. 6.

In both the structures shown in FIGS. 1 and 2, the metal core 2 is provided in the center. The metal core 2 is formed of metal or metal alloy, for example, and has a thickness of approximately 50 μm to 500 μm. The metal core is formed of Cu or mainly composed of Cu or is formed of Al or mainly composed of Al. (Here, “the metal core is mainly composed of metal” means that most of the metal core is formed of a metal material, impurities are contained therein on the order of ppm, and the characteristics are improved.)

When the metal core is used in a set having reduced weight, thickness, length, and size and required to have a heat radiation property, it is preferable that the metal core 2 is formed of Al or mainly composed of Al. The Al material is lightweight although the thermal conductivity is slightly inferior to Cu, and in the Al material, a hard ceramic film having rigidity can be formed in a self-generating manner. The ceramic film formed in a self-generating manner is a reaction product of a metal material formed by chemical treatment and is, for example, an alumina film formed by anodization. The alumina film has a high hardness, and the rigidity can be increased by the film thickness.

The insulating resin film 4A is formed on the surface of the ceramic film CEa formed on the front surface of the metal core 2, and the insulating resin film 4B is formed on the surface of the ceramic film CEb formed on the rear surface of the metal core 2. Since the ceramic film CE is brittle and easy to break, the surface of the ceramic film CE is coated with the insulating resin film 4, and the drawbacks are solved. Since the rigidity of the element mounting substrate 1 is increased by the ceramic film CE, a filler may not be mixed in the insulating resin film 4. If a glass fiber or the like is woven into the insulating resin film 4, or a filler is mixed therein, the glass fiber or the filler may become dust in the dicing.

A square (frame) at the outermost periphery shown by a dotted line in FIGS. 1 and 2 is the outer shape of the element mounting substrate 1 and corresponds to a dicing line DC1 shown in FIGS. 4A and 6C. The ceramic film CE is arranged inside the dicing line DC1, and the metal core 2 is not exposed directly at the end surface of the element mounting substrate 1 to thereby improve a withstand voltage.

As shown in FIG. 4B, when the metal core substrate is directly diced without forming the ceramic film CE on the side surface of an individual piece of the element mounting substrate, the metal core substrate is diced in an area shown by a thick dashed line (DC2) in FIG. 1B. In this case, the metal core substrate M is exposed directly at the end surface of the element mounting substrate 1. In this structure, since the metal core substrate is exposed directly at the end surface of the element mounting substrate, a high level of heat radiation property is obtained.

The conductive pattern 5A is formed on the surface of the insulating resin film 4A, and the conductive pattern 5B is formed on the surface of the insulating resin film 4B. The conductive pattern 5A is constituted of an island on which a semiconductor element is mounted, an electrode connected to the semiconductor element, a passive element, and so on, and a wiring extended integrally with the island or the electrode. Although the conductive pattern 5B is mainly an external electrode, the island, the electrode, the wiring, and so on may be provided.

Although FIG. 1 shows double-layered metal wiring structure in which the wiring layers except for the metal core are the wiring layer 5A and the wiring layer 5B, there may be provided a structure in which the insulating resin film and the conductive pattern are repeatedly stacked on the front and rear sides to form four layers, six layers, eight layers, and more.

In FIG. 3, the example of the structure shown in FIGS. 1A and 1B is more specifically described. FIG. 3A is a perspective view. FIG. 3B is an A-A cross-sectional view of FIG. 3A. FIGS. 4A and 4B are views for explaining a state of the metal core substrate in the dicing. FIG. 5A is a cross-sectional view showing a state in which an element EL is embedded in the element mounting substrate.

In the embodiment shown in FIG. 3, as shown in FIG. 3B, the four conductive patterns are provided, and, as shown in FIG. 3A, the four through-holes 3 are provided on the single metal core substrate M, for example. In the element mounting substrate, the element EL is embedded in an opening portion OP. The element EL may be a semiconductor bear chip or may be a SIP in which a plurality of semiconductor elements and passive elements are one package. Particularly in the SIP, since the number of terminals to be connected to the electrode of the metal core substrate is reduced, the reliability is improved. For example, when an IC bear chip and a transistor are embedded in a bared manner, the number of terminals of IC and three terminals of the transistor are required as connection. However, a plurality of elements sealed in one package are embedded as shown in FIG. 5B, whereby the number of the terminals to be connected of the package and the metal core substrate is reduced. The embedded elements EL are arranged while being slightly shifted from the center as shown in FIG. 3A. The dotted lines of FIG. 3A having an arrow at one end and perpendicular to each other are the vertical and horizontal centerlines of the element mounting substrate, and the intersection is the center of the element mounting substrate. As seen from the drawing, the element EL is arranged while being shifted from the intersection as the center.

FIG. 4A shows a separation method. Each of the metal cores 2 is constituted of a single plate-like substrate, and the metal cores are arranged in the form of a matrix. The solid arrows arranged in the vertical direction are the dicing lines. In this example, the metal core 2 is not directly diced, and the insulating resin film 4 provided between the metal cores 2 is diced to be separated. According to this constitution, the metal core 2 is not exposed on the side surface of the element mounting substrate 1 as shown in FIGS. 1A and 2B, and, at the same time, since the ceramic film which is a self-generated film including the side surface is formed, the withstand voltage property is improved.

FIG. 4B shows a different separation method from the one shown in FIG. 4A. In the present embodiment, the outer solid line shows the single metal core substrate M. An area that can normally realize four element mounting substrates is previously provided on a single metal substrate, and the metal core substrate M itself is directly diced afterward. In this case, since the metal core substrate M is not required to be previously separated as in the embodiment of FIG. 4A, it is simple as a manufacturing method. The metal core 2 is exposed on the side surface of the element mounting substrate 1 after dicing, and a high level of heat radiation property is obtained.

FIG. 6 shows another embodiment of the present invention. FIG. 6A is a perspective view. FIG. 6B is an A-A cross-sectional view of FIG. 6A. FIG. 6C is a view showing a state of a metal core substrate in the dicing. FIG. 6D is a cross-sectional view showing a state in which the element EL is embedded in the element mounting substrate.

As shown in FIG. 6A, four large and small metal core substrates MA to MD are embedded into the single element mounting substrate 1. In the ceramic film which is a point of the present invention in which a portion between the metal core substrates diced into individual pieces is embedded with the insulating resin layer 4, all the front, rear, and side surfaces of the metal core substrate are coated with the ceramic film, and the rigidity of each of the metal core substrates M is improved. However, since a portion between the adjacent metal core substrates M is constituted of the insulating resin layer 4, the metal core substrate M is inevitably easily folded at the portion. Thus, in the present invention, the insulating resin film 4 between the metal core substrates M adjacent to each other is not extended from one side of the element mounting substrate to the opposing side, and the metal core substrate M is arranged in the middle thereof, so that the insulating resin film 4 is blocked there. For example, the insulating resin film 4 between the metal core substrate MA and the metal core substrate MB is blocked by the metal core substrate MC as shown by the arrow A in FIG. 6A. Similarly, the insulating resin film 4 between the metal core substrate MA and the metal core substrate MC is blocked by the metal core substrate MB as shown by the arrow B. The insulating resin film 4 between the metal core substrate MC and the metal core substrate MD and the insulating resin film 4 between the metal core substrate MB and the metal core substrate MD are blocked by another metal core substrate M as shown by the arrows C and D, respectively. Although the weak portion of the element mounting substrate shown in FIG. 6A corresponds to the arrow extending direction in which the metal core substrate M is not present, the metal core substrate M is present in the middle from one side of the element mounting substrate to the opposing side, and therefore, the substrate is prevented from being broken or bent at once from one side of the element mounting substrate to the opposing side.

In the element mounting substrate shown in FIG. 6A, a portion of the metal core substrate MC is eliminated, and the element EL constituted of a bear chip or a SIP is embedded into the element mounting substrate as shown in FIG. 6D. In the three metal core substrates MA, MC, and MD, the metal core 2 is exposed at portions shown by point circles (contact holes opening in the insulating resin), and, as shown in FIG. 6B, the wiring on the substrate and the metal core 2 are in contact with each other through the hole.

Thick arrows of FIG. 6C show the dicing lines and show that the metal core substrate is arranged to be retracted inward from the side of the element mounting substrate. According to this constitution, the metal core substrate M is not exposed on the side surface of the element mounting substrate 1, and, at the same time, since the ceramic film which is a self-generated film including the side surface is formed, the withstand voltage property is improved.

In the above structure described in FIG. 2, the metal core substrate is separated, and the through-holes are formed at the separating portion to form a via there, whereby a hole penetrating through the metal core substrate is not required to be formed. Therefore, while the formation of the through-hole is easy, as described above, according to the present embodiment, the metal core substrate is utilized as a relay of the via, and therefore, the metal core substrate can be separated at a portion requiring electrical separation. Therefore, the hole penetrating through the metal core substrate is not required to be formed, and since the depth of the via becomes small, a fine via is easily formed.

Next, a method of manufacturing the element mounting substrate shown in FIG. 1B is described using FIGS. 9 to 13.

FIG. 9A is a plan view of the metal core substrate Min the method of manufacturing the element mounting substrate. FIG. 9B is an A-A cross-sectional view of FIG. 9A. FIG. 9C is a B-B cross-sectional view of FIG. 9A.

First, the plate-like metal core substrates M provided on the single element mounting substrate 1 are arranged in a planar manner in the vertical and horizontal directions and integrated by connecting pieces 30A and 30B extending in the vertical and horizontal directions, respectively. The metal core substrate M shown in FIG. 9A is formed as follows. First, the metal core 2 is formed by pressing or etching a metal sheet or a metal foil. Next, as shown in FIGS. 9B and 9C, the ceramic film is formed in a self-generating manner on the front, rear, and side surfaces of the metal core 2. According to the above, the metal core substrate M shown in FIG. 9A is formed. At that time, the through-holes 3 are formed as shown in FIG. 9C (B-B cross section of FIG. 9A), and the ceramic film CE is formed on the inner side wall of the through-hole 3. When it is considered to separate into the element mounting substrates 1 by, for example, dicing with a rotating blade, laser dicing, or press cutting to be performed later, it is preferable that a self-generating film is not formed at a portion of a connecting piece corresponding to a separation line.

Subsequently, the insulating resin film is formed on the surface of the ceramic film. FIG. 10A shows a state in which the insulating resin film 4 is formed on the cross section shown in FIG. 9B. FIG. 10B shows a state in which the insulating resin film 4 is formed on the cross section shown in FIG. 9C.

As shown in FIGS. 10A and 10B, the front and rear surfaces of the metal core substrate are in a flat state and covered by the ceramic film and the insulating resin film, and the side surface of the metal core substrate and the side wall of the through-hole 3 are coated with the ceramic film and the insulating resin film, as well.

Subsequently, as shown in FIG. 11, through-holes are formed. FIG. 11A is a plan view. FIG. 11B is an A-A cross-sectional view of FIG. 11A. FIG. 11C is a B-B cross-sectional view of FIG. 11A. The through-holes are formed by forming a second through-hole 3A having a smaller diameter than the through-hole 3, while remaining the ceramic film and the insulating resin film 4 formed on the side wall of the through-hole 3. Since the area where the second through-hole 3A is formed is constituted only of the insulating resin film, the through-hole 3A can be easily formed by a laser, a drill, or a punching machine. In the side wall of the through-hole 3 and the side wall of the metal core substrate, the outer side of the metal core substrate is doubly coated with the ceramic film and the insulating resin film.

Further, as shown in FIG. 12, a conductive material is embedded in the second through-hole 3A with plating, conductive paste, or solder, for example. According to this constitution, the conductive pattern 5A on the front surface of the element mounting substrate to be formed later and the conductive pattern 5B on the rear surface are electrically connected. The conductive pattern 5A and the conductive pattern 5B may be electrically connected by forming a conductive film on the side wall of the second through-hole 3A, or a conductive paste such as Ag, plating, and so on may be filled in the second through-hole 3A.

Finally, although not illustrated, a portion corresponding to the connecting piece is separated by a press, laser dicing, or dicing with a rotating blade. The completed element mounting substrate is shown in FIG. 13 and corresponds to a portion shown by the dotted line in FIGS. 9A and 11A. The insulating resin layer 4 is exposed on the end surface of the completed element mounting substrate, and the side walls of the connecting pieces 30A and 30B appear from a portion thereof. When the element mounting substrate is diced into individual pieces, only a connecting piece portion having a small width is formed of a metal material, and therefore, the burden on a blade and so on is small, and the metal core substrate can be easily separated.

The semiconductor element is mounted on the element mounting substrate, and the semiconductor module is provided. The semiconductor element of the semiconductor module is sealed with an insulating resin, and the semiconductor device is provided.

Hereinafter, the result of the estimation of the film structure of the ceramic film adopted in the present application is shown.

First, there will be described a method of observing the film structure of the ceramic film in a plane in which a film-thickness direction of an alumina film as an example of the ceramic film is a perpendicular.

FIG. 14 is a perspective view for explaining a method of observing the film structure of the alumina film in the plane in which the film-thickness direction of the alumina film as an example of the ceramic film is a perpendicular. FIG. 15 is a SEM photograph in which the film structure is observed.

As shown in FIG. 14A, samples in which an alumina (Al₂O₃) film is formed on an aluminum (Al) film are provided. Among the samples, the alumina film is cut out using FIB (Focused Ion Beam), and the plane in which the film-thickness direction in the alumina film is a perpendicular is exposed on the surface. As shown in FIG. 14B, the surface is photographed in the arrow direction to obtain a SEM photograph.

FIG. 15 is the SEM photograph. FIGS. 15A and 15B are SEM photographs of an alumina film formed using a submerged plasma process. FIG. 15C is a SEM photograph of an alumina film formed by an anodic oxidation method for comparison. The SEM photograph of FIG. 15B is obtained by increasing the magnification (ten-thousand times) of the SEM photograph of FIG. 15A. The SEM photographs of FIGS. 15B and 15C are obtained at the same magnification (one hundred-thousand times).

As shown in FIG. 15C, it can be shown that while the alumina film formed using the anodic oxidation method has a porous layer in which a large number of holes are formed on the entire surface, the alumina film formed using the submerged plasma process does not have the porous layer in which minute holes are formed on the entire surface. From this, it can be shown that the alumina film formed using the submerged plasma process is a more dense film and has a high rigidity, and fine alumina pieces are less likely to be formed.

Accordingly, since the alumina film formed by the submerged plasma process has a high rigidity, the film thickness can be reduced, and thus the entire thickness of the element mounting substrate can be reduced.

INDUSTRIAL APPLICABILITY

Since the present invention is an element mounting substrate using as the core material the material in which the ceramic films are formed on the front and rear surfaces of the metal substrate, the element mounting substrate is mounted on a set having reduced weight, thickness, length, and size in the future, and a high rigidity and a heat radiation property can be realized simultaneously.

DESCRIPTION OF REFERENCE NUMERALS

-   1 Element mounting substrate, 2 Metal core, 3 Through-hole, 4     Insulating resin, 5 Conductive pattern, M Metal core substrate, MG     Margin, DC Dicing line 

1-12. (canceled)
 13. An element mounting substrate comprising: a metal core mainly composed of metal; a first ceramic film formed on one main surface of the metal core; a second ceramic film formed on the other main surface of the metal core; a first insulating resin film formed on a surface of the first ceramic film; a second insulating resin film formed on a surface of the second ceramic film; a first conductive pattern formed on a surface of the first insulating resin film; and a second conductive pattern formed on a surface of the second insulating resin film, wherein the first ceramic film and the second ceramic film have a smaller thermal expansion coefficient than the metal core.
 14. The element mounting substrate according to claim 13, wherein thickness of the first ceramic film is larger than thickness of the metal core.
 15. The element mounting substrate according to claim 13, wherein thickness of the second ceramic film is larger than the thickness of the metal core.
 16. The element mounting substrate according to claim 13, wherein the metal core is formed of metal mainly made of Al, and the first ceramic film and the second ceramic film are mainly composed of an Al oxide film.
 17. The element mounting substrate according to claim 13, wherein the metal core comprises a through-hole, and an inner wall of the through-hole is coated with a ceramic film having the same components as the first ceramic film or the second ceramic film.
 18. An element mounting substrate comprising: a metal core formed of a metal sheet having a front surface, a rear surface, and a side surface located around the front and rear surfaces; a first through-hole provided at a portion of the metal core; an insulating resin coating the front and rear surfaces of the metal core and, at the same time, filling the first through-hole; a first conductive pattern provided on an insulating resin surface coating the front surface of the metal core; a second conductive pattern provided on the insulating resin surface coating the rear surface of the metal core; a second through-hole provided inside the first through-hole and provided at a portion of the insulating resin embedding the first through-hole; and an embedded portion provided in the second through-hole and electrically connecting the first conductive pattern and the second conductive pattern, wherein the front and rear surfaces of the metal core and the inner wall of the first through-hole have a self-generating film containing as one component the main component of the metal core and improving the rigidity of the entire element mounting substrate.
 19. An element mounting substrate comprising: a metal core in which a plurality of metal sheets having a front surface, a rear surface, and a side surface located around the front and rear surfaces are arranged on the same plane; an insulating resin coating the front and rear surfaces of the metal core; a first contact hole provided at a portion of an insulating resin coating a front side of the metal core and making the front surface of at least one of the metal sheets, constituting the metal core, exposed therefrom; a first conductive pattern electrically connected to the metal sheet through the first contact hole and provided on the front surface side of an insulating resin coating the front side of the metal core; a second contact hole provided at a portion of an insulating resin coating the rear surface of the metal core and making the rear surface of at least one of the metal sheets, constituting the metal core, exposed therefrom; and a second conductive pattern electrically connected to the metal sheet through the second contact hole and provided on the rear surface side of the insulating resin coating the rear surface of the metal core, wherein the front and rear surfaces of the metal sheet have a self-generating film containing as one component the main component of the metal sheet and improving the rigidity of the element mounting substrate.
 20. The element mounting substrate according to claim 19, wherein thickness of the self-generating film is larger than thickness of the metal sheet.
 21. The element mounting substrate according to claim 19, wherein the metal sheet is formed of metal mainly made of Al, and the self-generating film is mainly composed of an Al oxide film.
 22. The element mounting substrate according to claim 21, wherein the metal core has a through-hole, and a discrete element or an IC element is embedded in the through-hole.
 23. The element mounting substrate according to claim 21, wherein a SIP (system in package) in which a plurality of semiconductor elements are sealed is embedded in the through-hole.
 24. A semiconductor module comprising: the element mounting substrate according to claim 13; and a semiconductor element mounted to be electrically connected to the first conductive pattern. 